Aseptic loosening
of a cemented acetabular component appears to be about three times more
common than loosening of the femoral component. Cement keyholes drilled
into the acetabulum have been recommended to improve this fixation but
the optimum positions and sizes of these holes have never been satisfactorily
determined. We investigated the diameter, depth and number of keyholes
to be drilled to maximise the failure torque in a model system (1).
A Taguchi experimental design (2) was used to identify
the most significant factors and to predict the best configuration of
keyholes within the constraints of the experimental test rig. One hole
at each of the pubic, iliac and ischial sites, of 12 mm diameter and 6
mm depth, was found to be the optimum configuration. The failure torque
was most strongly dependent on the hole diameter in the pubic region,
decreased with increasing hole depth and was not sensitive to the number
of holes. Finite element modelling and mechanical testing of a single
keyhole was also performed to determine the ways in which individual holes
fail and the effects of depth and diameter.
References
1) Mburu G, Aspden RM, Hutchison JD. Optimising the configuration
of cement keyholes for acetabular fixation in total hip replacement using
Taguchi experimental design. Proc Instn Mech Engrs [H], J Eng Med 1999;
213:485-492.
2) Dar F, Meakin JR, Aspden RM. Statistical methods in
finite element analysis. J Biomech 2002; 35:1155-1161.
Department of Orthopaedics, University of
Aberdeen
